1. Field of the Invention
The present invention relates to a digital data modulating method in the digital communication.
2. Description of Related Art
There are two different modulating systems in the digital communication, that is, an FSK system and an FM system.
As seen from FIG. 6, in the FSK system pieces of data information representing logic "1"s are converted into signals of high-frequency f.sub.H whereas pieces of data information representing logic "0"s are converted into signals of low-frequency f.sub.L.
As seen from FIG. 7, in the FM system pieces of data information representing logic "1"s are represented by frequency-modulated signals of frequency 2f whereas pieces of data information representing logic "0"s are represented by frequency-modulated signals of frequency if. In FIG. 7 clock pulses and data pulses are indicated by C and D respectively.
The FSK system has a demerit of preventing its communication rate from increasing beyond a predetermined limit. The FM system has a demerit of the duty ratios of the modulated signals being sensitive to noise signals appearing in communication mediums, thereby often preventing required communications.
In view of these there has been an ever increasing demand for a digital data modulating method guaranteed free of distortion of duty ratio caused by noise signals appearing in communication mediums, thus assuring the stable communication, and permitting required demodulation of modulated signals even if their duty ratios are disturbed, and permitting the increasing of the communication rate.